<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>

        article {
            width: 1200px;
            margin: 0 auto;
            border: 2px solid black;
            overflow: auto;
            padding: 20px;
        }

        article > div {
            width: 32%;
            height: 50px;
            border: 1px solid red;
            box-sizing: border-box;
            float: left;
            text-align: center;
            line-height: 50px;
            margin: 3px 6px;
        }

    </style>
</head>
<body>
<article>
    <div>1</div>
    <div>2</div>
    <div>3</div>
    <div>4</div>
    <div>5</div>
    <div>6</div>
    <div>7</div>
    <div>8</div>
    <div>9</div>
</article>
</body>
</html>